title: [A case of previously undiagnosed methemoglobinemia exhibiting sustained low SpO2 value at the induction of general anesthesia].
abstract: A 70-year-old woman was scheduled to undergo surgery for removal of thyroid tumor under general anesthesia. A routine preoperative evaluation confirmed that the patient was stable with no signs of cyanosis and dyspnea. However, during pre-oxygenation as well as mechanical ventilation with 100% oxygen, she showed sustained low SpO2 values (i.e., 91%). Arterial blood gas analysis at FIO2 of 1.0 showed an oxygen partial pressure (PaO2) of 297 mmHg. Unexpectedly, the analysis revealed methemoglobinemia (MetHb concentration: 15%) causing a discrepancy between the low SpO2 and normal PaO2 values in this patient. Methemoglobinemia is an uncommon cause of cyanosis; however, anesthesiologists should be aware that some drugs used during perioperative period (e.g., local anesthetics) can cause methemoglobinemia. While our case was a mild one and the patient recovered with no complications, methemoglobinemia levels above 30% could cause tissue hypoxemia and, thereby, requiring a treatment with methylene blue or ascorbic acid.
authors.affiliation: Department of Anesthesiology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka 537-8511.
authors.forename: Rie
authors.initials: R
authors.lastname: Ono
authors.forename: Hironobu
authors.initials: H
authors.lastname: Tanigami
authors.forename: Kiyokazu
authors.initials: K
authors.lastname: Kagawa
authors.forename: Motomu
authors.initials: M
authors.lastname: Shimaoka
authors.forename: Shunji
authors.initials: S
authors.lastname: Sonoda
authors.forename: Akira
authors.initials: A
authors.lastname: Iura
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Yasue
authors.forename: Naho
authors.initials: N
authors.lastname: Hamabe
authors.forename: Asami
authors.initials: A
authors.lastname: Ishii
mesh_terms: D000368:Aged; D000768:Anesthesia, General; D005260:Female; D006801:Humans; D008708:Methemoglobinemia / Q000175:diagnosis*; D010092:Oximetry; D010100:Oxygen / Q000032:analysis; D013964:Thyroid Neoplasms / Q000601:surgery
chemical_list: D010100:Oxygen